Project Details
Projekt
Microlattice structures for lithium-ion battery electrodes: Chemo-mechanical beam modeling of diffusion-induced instabilities and optimal design
Subject Area
Mechanics
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 460684687
Recent progress in advanced fabrication such as 3D printing allows implementation of complex 3D microlattice structures as lithium-ion battery materials and unit cells. With large surface area, short diffusion paths and high stress relaxation, these structures offer significant performance improvement. However, due to lithiation-induced expansion, the slender ligaments of beam-lattices are prone to mechanical instabilities such as buckling. Such chemically induced nonlinear instabilities and their impact on the electrochemical performance of the electrode are insufficiently understood, let alone the optimal design of electrode microlattices. While current multi-physical simulation of lithium-ion batteries is mainly based on computationally expensive solid models, efficient simulation and optimization schemes based on multi-physical beam formulations are desirable for both instability analysis and electrode design. The objective of this joint proposal is to develop such methods by using beam formulations for the chemo-mechanical study of microlattice structures as battery electrode materials. We plan to first develop multi-physical beam formulations and discretizations coupling mechanics and transient ion diffusion. For materials subject to relatively small elastic strains such as Lithium manganese oxide or Vanadiumpentoxid, a geometrically exact, co-rotational 3D beam model will be extended with ion diffusion, swelling, and variation of material parameters with ion concentration. To address cross-sectional diffusion, both a simple heuristic model and an advanced warping-like model will be developed. For materials subject to potentially large deformations such as Silicon, a finite strain solid beam element with hyperelastic material laws will be extended to couple transient ion diffusion both axially and through the cross-sections. In view of structural optimization, the proposed beam and solid-beam elements will be implemented using isogeometric discretizations. To ensure the reliability and assess the efficiency of these models, they will be verified by chemo-mechanical 3D solid finite element simulations. Based on these beam formulations, a framework for the reliable chemo-mechanical analysis of buckling and post-buckling behavior of battery microlattice structures will be developed. The expected efficiency of the beam models should allow even simulations of samples with large numbers of unit cells to demonstrate both local and global buckling patterns and their dependency on charging rates, as well as geometric and material parameters. The framework will then be used to analyze the impact of buckling effects on battery performance such as capacity and voltage-state of charge curves. Using gradient-based optimization algorithms with adjoint sensitivities, we will obtain optimal microlattices with spatially varying strut thickness, material composition, or optimally curved struts that facilitate specific buckling behaviors to enhance performance
DFG Programme
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